Dell PowerConnect B-FCXs Configuration Manual page 634

17
Classification
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Given the variety of different criteria, there are many possibilities for traffic classification within a
stream of network traffic. For this reason, the priority of packets must be resolved based on which
criteria takes precedence. Precedence follows the scheme illustrated in
Figure
Determining the trust level of a packet
Figure 112
packet. As shown in the flowchart, the first criteria considered is whether the packet matches on an
ACL that defines a priority. If this is not the case and the MAC address of the packet matches a
static entry, the packet is classified with the priority of the static MAC entry. If neither of these are
true, the packet is next classified with the 802.1p CoS value, ingress port default priority, or the
default priority of zero (0).
592
Static MAC address
Layer 2 Class of Service (CoS) value – This is the 802.1p priority value in the Ethernet frame. It
can be a value from 0 through 7. The 802.1p priority is also called the Class of Service.
Layer 3 Differentiated Services Code Point (DSCP) – This is the value in the six most significant
bits of the IP packet header 8-bit DSCP field. It can be a value from 0 through 63. These values
are described in RFCs 2472 and 2475. The DSCP value is sometimes called the DiffServ value.
The device automatically maps the DSCP value of a packet to a hardware forwarding queue.
Refer to "Viewing QoS settings"
ACL keyword – An ACL can also prioritize traffic and mark it before sending it along to the next
hop. This is described in the ACL chapter in the section
112.
illustrates how PowerConnect B-Series FCX devices determine the trust level of a
on page 608.
"QoS options for IP ACLs"
PowerConnect B-Series FCX Configuration Guide
on page 579.
Figure through
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